12 Answers

Buy some throttle body cleaner. Clean your throttle body and Idle Air
Control valve. If no idea how to clean, replace the IAC. I think they are
around $50. Here is a video on how to clean the throttle body:
https://www.youtube.com/watch?v=oc7rnzYV-MY If no change after
cleaning, you may need a new EGR also.

The trouble with error codes is that they don't usually pin point the
problem. It will say "misfire" on cylinder one or two. Okay, so I have a
misfire. The problem is it never says, "Misfire due to spark plugs". It
now becomes a guessing game on what could be causing the misfire.
It could be vacuum leaks, bad EGR, dirty injectors, clogged Cat, bad
coils, bad plugs. Now you are faced with testing or replacing each
possible bad part. That's why when you take it to a shop they will say
things like, "we got a misfire code so we replaced XY and Z". Then a
week later the check engine light comes back on, with the same code.
Sometimes it's more than one component that can fail, giving the
misfire codes. I am driving around right now with 6 error codes on my
Camry. Toyota gave me the "we don't really know what the cause is,
so we will have to start tearing everything off the car to find it." I said,
yeah, no thanks. You will run me up $1000 in labor. I then drove my
car from Las Vegas to Montreal. I made it with no problems....but I
still have all the codes that I will figure out for myself. If I were you, I
would take the error code, for example PO302, look it up in the
internet, write down the causes, and just start testing or replacing the
needed parts. Otherwise, you will just be paying someone $85 an hour
to do the exact thing you will be doing.

Yeah i have been down this road
before.thought maybe I would get
lucky and there would be an exact
code.car needs state inspection as
of 2 days ago so I'm kinda
scrambling.hard to work ,plow take
care of house and work on vehicle in
sub zero weather with 5 ft snow as
I'm sure you all know.on top of that
my check engine light came on in my
07 f150 on my way home from work
today.but thanks for the advise

its not a guessing game.
the codes give you a general indication of WHERE the problem exists. The rest requires researching probable causes and testing the components. This is a process of elimination.
Each component you test will reduce the list of probable causes until you come to the likely culprit.
for example, a P0301 code on a grand marquis is a cylinder 1 misfire.
once you know this, you have to start testing the components involved. There is the spark plug, the coil on plug, and other components that could contribute to the issue. each has to be tested and eliminated.
its the same process the mechanic will use at any garage for 50+ dollars per hour.
Never try to fix your vehicle by "guessing" what the problem is. Thats a waste of time and money. If you have the patience then all you need is the proper tools to help diagnose the problem.
Its a great way to get to know your vehicle and take pride in maintaining it.

Like I said, error codes never give a definitive answer. A process of
elimination is just guessing on where to start. If you have a list of 15
possible causes, aren't you pretty much guessing on where to start
the process of elimination? I realize it gives you a general direction.
Testing various components also takes various tools and gadgets. All
of which add up very quickly. I'm not saying that you'll never figure it
out. How many times have you heard people say that they have
brought their car to the shop, and they've spent $400 on repairs and
still have the same problem? That's because the shop doesn't want to
spend the time and effort to go through all 15 items and test them all.
They just guess and throw parts at it. I just wish that the code
systems would narrow it down to a specific issue instead of a whole
laundry list.